This proposal will map the changes in the distribution of glycoproteins on the surface of the preimplantation mammalian embryo with the objectives of pinpointing (l) the times and (2) the locations of membrane changes involved in the development of trophoblast. The specific aims of the research will be (l) to determine when glycoproteins become localized to the apical and/or basal surfaces of the trophoblast cells using ferritin-lectin labelling techniques in conjunction with electron microscopy, (2) to biochemically characterize the apical and basal glycoproteins by I125 lebelling and electrophoretic analysis, (3) to determine if cell-cell contact is required to initiate cell surface and cortical cytoplasmic changes during compaction with micromanipulation techniques followed by scanning and transmission electron microscopy, and (4) to study the roles of microvilli and microtubules in cell spreading with specific drug inhibition followed by light and electron microscopic analyses.